A novel method to improve the critical damage parameter of powder metallurgical components during the cold upsetting

In the metal forming process, the understanding of metal flows and the fracture strains are most significant to the failure/damage of the components. Usually, in metalworking, damage occurs because of nucleation, growth and coalescence of the void into a small fracture. These small fractures increased in the circumferential path due to the existence of stresses and the pores which leads to failure at the equatorial position during the upsetting of porous samples. Hence, the fracture of the workpieces strongly depends on the stresses and the pores. Such form of stresses and pores if relieved will give a better damage limit of the material. Therefore, in this research, a novel scheme of localised heating is adopted at the equatorial position of the compressed samples to enhance the critical damage parameter. The powder metallurgy route was used to prepare the required compacts with different relative densities (80%–90%) and 1 aspect ratio by applying suitable powder forming pressures. The upsetting test was performed on the obtained porous samples for various weight percentages of titanium (2%–6%) in the aluminium at the stable strain rate (0.1 s−1) and the damage location was noticed for various components. After the identification of damage position, various temperatures (100 °C–250 °C) of localised heating were attempted on the failure site of the specimens after some incremental stages of upsetting tests. The experimental results were analysed using various damage criteria and it was found that the initiation of failure is delayed and increased the critical damage value by selectively heating the samples because of relieving the stresses, reduction in porosity and changes in microstructure.

Effectiveness of geocell wall, geogrid and micropile anchors for mitigation of unstable slopes

Slope failure mitigation practices are well developed in recent years. Recently, geosynthetic, geocell, and geogrid combined with micropiles are being used extensively in various slope stabilization works. But integrated approaches are still lacking. In this study, a method of slope stabilization is proposed by integrated use of micropile, geocell and geogrid from an engineering and economical point of view. The study was done on slope failure located at Chandragiri Hill, south west of Kathmandu, Nepal. Geotechnical problems of the site, the design of geocell foundation, micropile and geogrid are done on the based on numerical analysis using Phase-2 software with field data. The results of analytical studies revealed that, the use of a combination of geocell, micropile and geogrid is beneficial in increasing slope stability. As per numerical analysis, in the slope failure site, geocell gravity walls each of 3.8 m, is constructed in different step. Beneath the geocell wall, different layers of geogrid were placed filled with granular materials. The geocell wall is connected with micropile from inside. The micropile works as an anchorage and support for geocell wall, which increases the stability of a failed slope.

Using OBR for pressure monitoring and BVID detection in type IV composite overwrapped pressure vessels

Type IV COPVs (Composite Overwrapped Pressure Vessels) are among the most suited structures for hydrogen storage. However, its complex modes of failure and requirement for periodic maintenance has led the industry to apply high safety factors on designs. This is one of the challenges inhibiting the widespread usage of the H2 in commercial vehicles. Structural health monitoring based on optical fibers is an emerging technology that can overcome these problems, as a neural network of sensors can be integrated to the structure during manufacturing and is readily accessible over the vessel lifetime. This gives information about the real structure condition, reducing overall maintenance costs. Here, core optical fibers were embedded in type IV COPVs during the manufacturing process and monitored with OBR (Optical Backscatter Reflectometer). Sensors were interrogated during an impact detection test and a pressurization test until burst failure. Fibers were capable of detecting the position and intensity of the damage in the first test and provided strain profiles over the entire length of the vessel for longitudinal and circumferential directions on the second. Optical microscopy of vessel sections showed matrix accumulation around the optical fiber as the main cause of sensor’s failure. During pressurization, steep peaks of strain in the dome regions from the early measurements indicated the burst failure site.

Optimization of ER8 and 42CrMo4 Steel Rail Wheel for Road–Rail Vehicles

Railway track maintenance services aim to shorten the time of removing failures on the railways. One of the most important element that shorten the repair time is the quick access to the failure site with an appropriate equipment. The use of road-rail vehicles is becoming increasingly important in this field. In this type of constructions, it is possible to use proven road vehicles such as self-propelled machines or trucks running on wheels with tires. Equipping these vehicles with a parallel rail drive system allows for quick access to the failure site using both roads and railways. Steel rail wheels of road-rail vehicles are designed for specific applications. Since the total weight of vehicle is a crucial parameter for roadworthiness, the effort is made to minimize the mass of rail wheels. The wheel under consideration is mounted directly on the hydraulic motor. This method of assembly is structurally convenient, as no shafts or intermediate couplings are required. On the other hand, it results in strict requirements for the wheel geometry and can cause significant stress concentration. Therefore, the problem of wheel geometry optimization is discussed. Consideration is given to the use of ER8 steel for railway application and 42CrMo4 high-strength steel. Finite element analysis within Ansys software and various optimization tools and methods, such as random tool, subproblem approximation method and first-order method are applied. The obtained results allow to minimize the rail wheel mass with respect to the used material. Moreover, computational demands and methods leading to the best results are compared.

Impact of Threading Dislocations Detected by KOH Etching on 4H-SiC 650 V MOSFET Device Failure after Reliability Test

In this study, the correlation between the Emission Microscopy (Em.Mi.) related to the failure site of the 4H-SiC 650V MOSFET devices after reliability test and epitaxial dislocation defects is presented. Devices failed at the High-Temperature Reverse Bias (HTRB) test were considered. Device layers have been stripped out by chemical wet etching and etched in a high temperature KOH solution to characterize defects emerging at the SiC surface. This approach was used to correlate failure emission spots with underlying structure of the material. KOH etching process on delayered devices was performed at 500°C for 10 minutes and then analysis by optical microscopy and SEM was carried out for defect classification and correlation with failure location.

Incidence and Mode of Deployment Failure of the Fast-Fix 360™ Meniscal Repair Device

Background Meniscal repair device deployment failure is a recognised complication of all-inside meniscal repair with subsequent risk of patient harm. The Fast-Fix device has undergone design changes to reduce deployment failure since its introduction in 2001. Purpose The purpose of this study was to assess the incidence and mechanism of intra-operative deployment failure of the 3 rd generation Fast-fix 360™ (Smith & Nephew, Andover, USA) device. Method Data was prospectively collected for 106 consecutive all-inside meniscal repairs undertaken with the Fast-fix 360™ device. Patient demographics, mechanism of failure, site and type of repair were recorded. Results 20 deployment failures occurred in 423 Fast-fix 360™ deployments, an incidence of 4.72%. Deployment failure occurred in 19 of 109 patients an incidence of 17.43%. Six different failure mechanisms occurred; anchor exiting device without trigger being initiated, anchors not holding in meniscus, both anchors simultaneously exiting device and braided suture failing. The most common failure mechanism was failure of the second anchor not holding in the meniscus. Average cost of device failure was $75 per patient. Conclusion Despite design modification, deployment failure still occurs with similar modes top to the original design.

Incidence and Mode of Deployment Failure of the Fast-Fix 360™ Meniscal Repair Device

Background Meniscal repair device deployment failure is a recognised complication of all-inside meniscal repair with subsequent risk of patient harm. The Fast-Fix device has undergone design changes to reduce deployment failure since its introduction in 2001. Purpose The purpose of this study was to assess the incidence and mechanism of intra-operative deployment failure of the 3 rd generation Fast-fix 360™ (Smith & Nephew, Andover, USA) device. Method Data was prospectively collected for 106 consecutive all-inside meniscal repairs undertaken with the Fast-fix 360™ device. Patient demographics, mechanism of failure, site and type of repair were recorded. Results 20 deployment failures occurred in 423 Fast-fix 360™ deployments, an incidence of 4.72%. Deployment failure occurred in 19 of 109 patients an incidence of 17.43%. Six different failure mechanisms occurred; anchor exiting device without trigger being initiated, anchors not holding in meniscus, both anchors simultaneously exiting device and braided suture failing. The most common failure mechanism was failure of the second anchor not holding in the meniscus. Average cost of device failure was $75 per patient. Conclusion Despite design modification, deployment failure still occurs with similar modes top to the original design.

Incidence and Mode of Deployment Failure of the Fast-Fix 360™ Meniscal Repair Device

Background Meniscal repair device deployment failure is a recognised complication of all-inside meniscal repair with subsequent risk of patient harm. The Fast-Fix device has undergone design changes to reduce deployment failure since its introduction in 2001. Purpose The purpose of this study was to assess the incidence and mechanism of intra-operative deployment failure of the 3 rd generation Fast-fix 360™ (Smith & Nephew, Andover, USA) device. Method Data was prospectively collected for 106 consecutive all-inside meniscal repairs undertaken with the Fast-fix 360™ device. Patient demographics, mechanism of failure, site and type of repair were recorded. Results 20 deployment failures occurred in 423 Fast-fix 360™ deployments, an incidence of 4.72%. Deployment failure occurred in 19 of 109 patients an incidence of 17.43%. Six different failure mechanisms occurred; anchor exiting device without trigger being initiated, anchors not holding in meniscus, both anchors simultaneously exiting device and braided suture failing. The most common failure mechanism was failure of the second anchor not holding in the meniscus. Average cost of device failure was $75 per patient.Conclusion Despite design modification, deployment failure still occurs with similar modes top to the original design.

Enhancing Point Defect Isolation by Using Ionizing Radiation

An application-specific integrated circuit (ASIC) for a high reliability application is found to have a missing sidewall spacer in a single transistor. Manufacturer burn-in and standard component electrical tests do not capture this defect. The defect manifests after exposure to ionizing radiation. Photon emission microscopy (PEM), laser voltage imaging (LVI), and laserassisted device alteration (LADA) are used to isolate the failure site. At the failure site a focused ion beam (FIB) cross section indicates that a doubly doped drain (DDD) (N+) is likely present where a lightly doped drain (LDD) is designated. This defect leads to a failure mode that is consistent with hot-carrier injection in complementary metal-oxide semiconductor (CMOS) transistors. This paper presents the testability from a fault isolation aspect, shmoo plot characterization, and backside optical techniques to identify its spatial location. A discussion of the results includes why ionizing radiation allowed the defect’s capture and potential implications of using ionizing radiation as a viable failure analysis technique.